iPhone 5S tracks your movement even with a dead battery

Ever since Edward Snowden unleashed the floodgates of just how far the tendrils or organisations like the NSA reach — and, perhaps surprisingly, the Xbox One's original vision for an always-on Kinect that can see in the dark — the internet at large is as concerned about privacy as it has ever been.

As if some kind of Twilight Zone or Black Mirror episode, the devices we're so worried about breaching our privacy are the ones we use and carry with us every single day, and even ask if it can use our locations on a regular basis.

You might think shutting off that device will prevent it from knowing exactly where you are, but a report on Reddit is now suggesting otherwise.

Redditor Glarznak relates a tale where he was travelling abroad, and his iPhone 5S battery died. Rather than immediately run to the nearest outlet like the majority of us would do (if we even allowed the battery to get far enough into the red, that is), he bravely tossed caution to the wind, and his dead phone into his satchel.

Upon returning home from the vacation, Glarznak recharged his phone. When loading up Argus, a fitness and motion tracker app for iOS, he noticed that Argus had actually recorded his steps throughout the vacation, despite the iPhone 5S having died. It would seem that, despite the battery being drained, the phone still tracks your movement.

While this may seem a bit terrifying — especially considering the shaky state of internet privacy in the past couple of years — there is what is likely a simple explanation.

When the iPhone 5S battery dies, it doesn't completely drain of power — there's a little bit left in reserve, and the phone automatically shuts itself off. The iPhone 5S also includes the M7 processor — a chip separate of the main SoC — which tracks motion data.

It would make sense for what is essentially a pedometer to use extremely little power, considering it'd be constantly running in the background. In all likelihood, the pedometer is just running unrelated to the rest of the phone, and when the phone powers back on, it grabs the data from the M7.

It's tough to know for sure, and Glarznak's experience is both impressive and a little scary, but the answer is probably not as terrifying as it may seem.